Halloween decorations? No! It’s Euonymus Caterpillars doing the decorating in May.
I received a call about plants totally covered in white webbing. Although it looks like Halloween decorations from the street, on closer inspections, caterpillars were present.
Referring to the 20 questions of Diagnostics, always start with “What is the Plant?”
In this case the plant was Winged Euonymus, Euonymus alatus. Euonymus across the street were unaffected but these were covered. The Euonymus caterpillar, Yponomeuta cagnagella (Lepidoptera: Yponomeutidae) is a European species that was first reported in North America in Ontario in 1967. The larvae (caterpillars) feed in colonies that envelop the foliage in large silken webs. They are defoliators of primarily Euonymus europaea, E. kiautschovicus, and E. alatus and can kill the shrub if heavy infestations occur year after year. The female moth lays eggs in mid- to late July and covers them with a gummy secretion that hardens into a shell that protects the eggs and newly hatched larvae. The eggs hatch in mid-August and the larvae immediately prepare to overwinter under their eggshell. There is no further activity until the following year, when larvae make small webs and feed on new leaves. Cocoon formation begins in late June and adult moths appear a few weeks later. There is only one generation per year. Larvae can be controlled with a single application of insecticide spray when the small webs appear in the spring.
We saw some Euonymus caterpillars last year in other parts of Lake County but very sporadic. So, the homeowner is not decorating early. Blame it on the cat,Euonymus Caterpillar that is!